Ultra-fine-grained thermoplastics

ABSTRACT

Ultra-fine-grained thermoplastics such as polyolefins, for example, having an average particle size D 50  of less than 400 μm and are present in a mixture along with a filler where the amount of filler material in the mixture amounts to 40 to 90% with respect to the mixture. As such ultra-fine-grained thermoplastics cannot be obtained by means of the normal milling process of if so then only with considerable expenditure, the process for manufacturing ultra-fine-grained thermoplastics is performed in such a manner that a mixture containing 10 to 60 wt. % thermoplastics with respect to the mixture and 40 to 90 wt. % filler material with respect to the mixture is ground e.g. in an impact pulverizer, as a result of which thermoplastic particles with an average particle size D 50  less than 400 μm are produced.

The present invention relates to ultra-fine-grained thermoplastics inground particulate form.

BACKGROUND OF THE INVENTION

It is known to employ thermoplastics in fine to ultra-fine-grainedparticulate form for various purposes. An ultra-fine-grained form isdesired if the thermoplastics have to be mixed as homogeneously aspossible with other substances. As the thermoplastics very oftenrepresent the more expensive component in the mixture, or thethermoplastic is only an additive but not the active ingredient, or theproperties of the thermoplastics have to be modified, an effort is madeto employ as little as possible of the thermoplastics in the mixture inquestion.

Thermoplastics cannot be readily divided into a finely divided form bygrinding, or if so only at great expense, and it is not possible toachieve average particle sizes smaller than 400 μm. Heat is releasedduring the grinding process and the thermoplastics, depending on theirtype, in particular those with adhesive or low melting pointcharacteristics, are immediately impossible to grind down. As a means ofavoiding this problem, it is known to employ cryogenic grindingprocesses. The material to be ground is cooled by liquefied nitrogenwhereby it becomes brittle and is subjected to grinding in this cooledstate. Also this process is limited with respect to particle fineness,and the yield is poor.

Precipitation processes are employed to produce thermoplastics, such aspolyolefins for example, in a finer grained form than is achievable bygrinding. These processes which enable thermoplastics to be produced inan ultra-fine form are multi-stage processes with long cycle times andalso emissions and large amounts of residual chemicals such ascontaminated precipitation medium or residual solvents. Consequently,products made by precipitation methods are expensive. Furthermore,various polymers are not suitable for producing in an ultra-fine powderform using precipitation processes.

SUMMARY OF THE INVENTION

The object of the present invention is to provide ultra-fine-grainedthermoplastics in ground particulate form and a process for theirmanufacture. The process should be simple and cost-favorable and theproducts should contain the thermoplastics in the desired particlesizes.

These objectives are achieved by way of the invention in that thethermoplastics exhibit an average particle size D₅₀ of less than 400 μmand are present in a mixture along with a filler where the amount offiller material in the mixture amounts to 40 to 90%.

Preferred are thermoplastics exhibiting an average particle size of 1 to400 μm, especially preferred is from 10 to 300 μm, usefully from 80 to200 μm and especially from 80 to 120 μm.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For example, thermoplastics of the polyolefin type are usefullyemployed. Examples of polyolefins are polyethylene, polyethylene of highdensity (HDPE, density greater than 0.944 g/cm³), polyethylene of mediumdensity (MDPE, density 0.926-0.940 g/cm³), linear polyethylene of mediumdensity (LMDPE, density 0.926-0.940 g/cm³), polyethylene of low density(LDPE, density 0.910-0.925 g/cm³), and linear polyethylene of lowdensity (LLDPE, density 0.916-0.925 g/cm³), polyproplyene, isotactic oratactic polypropylene, crystalline or amorphous polypropylene ormixtures thereof, poly-1-butene, poly-3-methyl-butene,poly-4-methylpentene. Further examples are copolymers or coextrudates ofthe above mentioned polyolefins and ionomeric resins such as e.g. thoseof polyethylene with vinyl-acetate (EVA) or acrylic acid, or e.g.ionomeric resins such as copolymers of ethylene with about 11% acrylicacid, methacrylic acid, acrylic esters, tetra-fluorethylene orpropylene, and also static copolymers, block copolymers orolefinpolymer-elastomer mixtures or ter-polymers e.g.ethylene-propylene-dien-caoutchouc (EDPM) oracrylnitril-butadiene-rubber/polypropylene (NBR/PP). Preferred arepolyethylenes and polypropylenes.

Especially preferred are low density polyethylene, linear low densitypolyethylene, high density polyethylene,ethylene-vinylacetate-copolomers (EVA),ethylene-acrylic-acid-acrylic-acid ester-terpolymers (EAA) orethylene-acrylic-acid-maleic-acid-anhydride terpolymers (EEAMA).

Advantageous are elastic and adhesive forms of polymers and inparticular polyolefins, as thermoplastic elastomers such as EPDM, NBRpolyisoprene or if desired natural rubber.

The filler material may be of a pure substance or a mixtures ofsubstances. The filler material or filler material mixture may containsubstances from the following examples or be comprised of suchsubstances.

Useful are filler materials containing or comprising the hydroxides,carbonates or oxides of aluminum, magnesium or calcium or mixturesthereof. Other filler materials are fillers of an inorganic or mineralnature from the series: talcum, vermiculite, perlite, mica, glasses,clays, silica, calcium sulphate, chalk, titanium dioxide, silicates,quartz, soot, graphite, metal powders such as e.g. Fe, Ni, Cr, Al, Cu,Zn etc., or mixtures containing the above-mentioned filler materials orcomprising the above-mentioned filler materials.

To the filler materials mentioned may be included also pigments such asinorganic or organic pigments. Examples of inorganic pigments are chalk,ochre, umber, green earth, graphite from the series of natural occurringpigments. Examples of synthetic inorganic pigments are white, black,colored and shiny pigments from the series including titanium white,lead white, zinc white, soot, iron oxide black, manganese black, leadchromate, red lead oxide, cobalt blue, ultramarine and others.

Examples of organic pigments are, apart from e.g. the naturallyoccurring bone black and indigo, the synthetic azo pigments, dioxazine,chinacridon, phtalocyanine, isoindolinon, perlene and perinon, metalcomplex and alkali blue pigments.

Examples of organic filler materials are cellulose type products such aswood powder, natural fibers, wool, cotton, flax, hemp, Chinese cane orsynthetic fibers.

The mixture according to the present invention may also contain otheradditives or additions such as stabilizers, anti-oxidants, softeners,lubricants, emulsifiers, antistatic agents, swelling agents, combustioninhibitors, so called modifiers, etc. The amount of additive oradditions may for example range from 0.001 to 10 wt. % with respect tothe above-mentioned mixture of thermoplastic and filler.

Preferred filler materials are the hydroxides and carbonates ofaluminum, magnesium and calcium and namely Al(OH)₃, Mg(OH)₂, Ca(OH)₂,MgCO₃ and CaCO₃.

The filler materials employed usefully exhibit an average particle sizeof 0.1 to 200 μm, preferably 1 to 100 μm.

In accordance with the invention the filler material content amounts to40 to 90 wt. % with respect to the mixture of thermoplastic and filler.Advantageously, the filler material content is 50 to 75 wt. % withrespect to the mixture. Correspondingly, the fraction of thermoplasticwith respect to the mixture lies at 10 to 60 wt. %, advantageously at 25to 50 wt. % with respect to the mixture.

The process according to the invention for manufacturing the ultra-finethermoplastics in ground particulate form is performed such that amixture containing the thermoplastics, comprising 10 to 60 wt. % of thefinal mixture, and the filler materials, comprising 40 to 90 wt. % ofthe final mixture, are ground in an impact pulverizer to an averageparticle size for the thermoplastics D₅₀ of 400 μm and less.

For example the thermoplastics are preferably ground to an averageparticle size of 1 to 400 μm, especially preferably to 10 to 300 μm andadvantageously to 80 to 200 μm and in particular to 180 to 120 μm.

The thermoplastics and fillers in general, and the preferred formsthereof, which are ground in mixture form are described in thefollowing.

The components of the mixtures such as the thermoplastics and thefillers and, according to the case in question also further additives,may be compounded or granular. Further, the components of the mixturemay be fed to a mixing facility such as an internal mixer or a twinscrew extruder or a single screw extruder or kneader and processed intoa homogeneous compounded mass. Masses made this way may e.g. besubjected to a pre-dividing step in a cutting mill.

As a rule the thermoplastic is melted and mixed with the fillermaterials e.g. in an extrusion or internal mill and, according to thecase in question, the additives mixed in and granulated in the plasticstate.

Immediately after compounding, it is useful to form a granulate e.g. bystrand granulation, hot precipitation, underwater granulating or bandgranulating.

If desired, granulating agents such as water and/or lubricants may beadded.

The components of the compounded masses may be subjected to the actualgrinding process as coarsely ground material or as previously preparedgranulate. Impact pulverizers are employed for this grinding process,e.g. conventional impacting pulverizers, hammer mills, impact platepulverizers, pinned-disk mills, beating mills or peening mills.

Preferred are beating mills, hammer mills, impact plate mills orpinned-disk mills.

During the grinding process the mill and/or as desired the materialbeing ground may be cooled. The cooling medium may be in the form ofgases, in particular air or nitrogen, liquids such as water, brine orliquid nitrogen. As a rule it suffices to keep the temperature of thematerial being ground at room temperature or e.g. at temperatures of -10to 40° C. or usefully from 10 to 30° C. and in particular from 15 to 25°C.

The products from the grinding process are therefore the thermoplasticspulverized to the desired size in a mixture along with the fillermaterial or mixture of filler materials.

As the thermoplastics are normally not used alone but e.g., exploitingthe adhesive, softening or sintering properties, fabricated along withthe filler materials into shapes of various forms, the mixturerepresents in fact an intermediate or even an end product.

It has also been found that these ultra-fine thermoplastics may beselected with a much larger particle size when incorporated in themixture e.g. 1.1 to 5 times larger, than would be possible using azurethermoplastic according to the present state-of-the-art.

After the grinding, the filler material may, if desired, be separatedfrom the ultra-fine thermoplastics by dissolution or by chemicalreaction.

For example, the ultra-fine thermoplastic may be employed in the form ofa mixture with the filler as a binding agent for highly filled moldingmaterials. Pure thermoplastics may often not be employed because of thecombustion behavior, thermal properties, mechanical properties orbecause of the price. For that reason efforts are made to replace thethermoplastics with larger quantities of e.g. cheaper or non-combustiblefillers. A larger fraction of filler material reduces the cohesion of amolding material itself or also between the molding material and theother materials in contact with it.. As a result of the ultra-finethermoplastic particles that can be achieved by way of the invention,these thermoplastic particles exhibit a high degree of homogeneity inthe mixture with the filler material. Consequently, a molding materialis achieved that exhibits excellent strength within itself and alsobetween such a molding material and a further material in contact withit, e.g. after extrusion or sintering.

The same advantages are obtained e.g. when using pigments such ascolored pigments as filler materials. On using the ultra-finethermoplastics in mixtures along with pigments as filler material highgrade powders for powder coating are obtained. Another application forthe ultra-fine particulate thermoplastics according to the inventionlies in the field of electrodes for batteries.

We claim:
 1. Ultra-fine-grained thermoplastics in ground particulateform, which comprises at least one ground thermoplastic material inmixture with a simultaneously ground filler wherein said thermoplasticis an ultra-fine grained thermoplastic which exhibits an averageparticle size D₅₀ of less than 400 μm and is present in a mixture alongwith said simultaneously ground filler where the amount of fillermaterial in the mixture amounts to 40 to 90%.
 2. Ultra-fine-grainedthermoplastics according to claim 1, wherein said thermoplastic exhibitsan average particle size of 10 to 300 μm.
 3. Ultra-fine-grainedthermoplastics according to claim 1, wherein said thermoplastic exhibitsan average particle size of 80 to 200 μm.
 4. Ultra-fine-grainedthermoplastics according to claim 1, wherein said thermoplastic exhibitsan average particle size of 80 to 120 μm.
 5. Ultra-fine-grainedthermoplastics according to claim 1, wherein said thermoplastic ispolyolefins or polyolefin-containing thermoplastics. 6.Ultra-fine-grained thermoplastics according to claim 1, wherein thefiller materials contain at least one of hydroxides, carbonates andoxides of at least one of aluminum, magnesium and calcium, and mixturesthereof.
 7. Ultra-fine grained thermoplastics according to claim 1,wherein said filler materials exhibit an average particle size of 0.1 to200 μm.
 8. Ultra-fine grained thermoplastics according to claim 1,wherein said mixture includes at least one additional additive in anamount of 0.001 to 10 wt. %.
 9. Ultra-fine grained thermoplasticsaccording to claim 1, wherein said mixture is ground at temperatures of-10 to 40° C.
 10. Ultra-fine grained thermoplastics according to claim1, wherein said filler material is a colored pigment.
 11. Ultra-finegrained thermoplastics according to claim 1, wherein said thermoplasticmaterial is a binding agent for molding materials.
 12. Ultra-finegrained thermoplastics according to claim 1, wherein said filler is amixture of filler materials.